1. Field of the Invention
The present invention relates to a toner for use in electrophotographic systems such as copying machines and printers, to a developer comprising the toner of the present invention, to an image-forming process cartridge comprising the toner of the present invention therein, to an image forming apparatus comprising the toner of the present invention therein, and an image-forming process using the toner of the present invention.
2. Description of the Related Art
Copying, recording, printing, and other image forming apparatus form latent electrostatic images by an electrophotographic system and develop the latent electrostatic images using a developer. These apparatuses have been more and more resource saving, miniaturized, high-speed and digitized. Developers for use in these apparatuses must have higher quality with higher reliability. In addition, such miniaturized apparatus must be operated at a further higher speed, while an image density (image quality) must be ensured. As possible solutions to these problems, a technique of increasing the speed of a development sleeve, a technique of increasing the concentration of a toner, and a technique of narrowing a development gap are known. However, the technique of increasing the speed of a development sleeve invites increased scattering of toner particles. In the technique of increasing the concentration of a toner, a carrier has decreased constraining force with respect to the toner, and the toner cannot be satisfactorily transported to a development region, thus inviting scattering of toner particles or toner deposition on the background of images. In particular, when a toner is prepared by a melting, kneading and pulverizing method, it is difficult to satisfactorily control the average particle diameter of the resulting toner, a toner having a small average particle diameter cannot be significantly efficiently prepared, and the resulting toner is often dispersed non-uniformly and has a broad charge distribution. Accordingly, a problem arises in that the conventional toner prepared by the melting, kneading and pulverizing method often invites scattering of toner particles and toner deposition on the background of images when the speed of the development sleeve increases or the concentration of the toner increases.
FIG. 2 is a sectional view of an image-developer in a related art.
The image-developer includes a developer-bearing member 11 with magnetic flux density distribution curves 11-1 and 11-2 of an development main magnetic pole P1 and of a developer-transport pole P5 in normal direction, a scatter-preventing member 12 with an elastic member (inlet seal) 37c made of, for example, polyurethane adhered with a double-faced adhesive tape. The image-developer also includes a development doctor 13 for controlling the amount of the developer on the developer-bearing member 11, a puddle 14 for transporting the developer to the front of the image-developer, and a transport screw 15 for transporting the developer to the rear of the image-developer.
In the conventional image-developer, when a magnetic blush made of a chain of magnetic particles of the developer is formed or disintegrated by action of magnetic force of the developer transport pole P5 disposed downstream from the development doctor 13, a weakly charged toner becomes separated from the carrier and scatters as indicated by a broken arrow in a circle in FIG. 3. An import seal 12a prevents to some extent but not completely the toner that separated from the carrier from scattering out of the image-developer. This phenomenon significantly depends on adhesion between the toner and the carrier. With reference to FIG. 4, the toner 20 and the carrier 30 adhere to each other by the van der Waals force and the Coulomb force. Of the two forces, the adhesion mainly depends on the Coulomb force, and scattering of the toner often occurs when the toner has a low charge “q” and tends to become separated form the carrier. Accordingly, the scattering of the toner particles often occurs when weakly charged toner particles increase in proportions in a charge distribution of the toner.
With reference to FIG. 5, the carrier and the toner on the surface of the developer-bearing member are transported at a linear velocity V=Rω, wherein V is the linear velocity, R is the radius of the developer-bearing member, and ω is the angular velocity of rotation. However, the linear velocity “v” of the tip of the magnetic blush is higher than “v” and is expressed by the equation: v=(R+H)ω, wherein “H” is a distance between the surface of the developer-bearing member and the tip of the magnetic blush. Thus, also from the mechanical viewpoint, the toner tends to scatter when the magnetic blush made of a chain of magnetic particles of the developer is formed or disintegrated. Some of recent miniaturized and higher-speed apparatus have a linear velocity on the surface of a developer-bearing member of 300 mm/sec or more, and the scattering of the toner particles becomes a more and more significant problem.
The scattering of the toner particles has been described above by taking the developer-transport pole P5 as an example. In the sharp line contact development system (SLIC development system), an angle “α” is set at 15° to 25°, wherein α(hereinafter referred to as “half-width”) is the angle formed between the rotational axis of the image carrier and a straight line between the points P and Q, wherein P and Q are each a point exhibiting a half value of the peak (maximum) value (gauss) with a point R exhibiting the peak value in the magnetic flux density distribution curve 11-1 of the development main magnetic pole P1 in FIG. 2. In the SLIC development system, the magnetic blush instantaneously forms and instantaneously disintegrates, and the linear velocity is higher than conventional equivalents. The scattering of the toner particles and toner deposition on the background of images in the development main magnetic pole P1 are significant problems.